The present invention is related to electromagnetic forming of metals, such as iron, steel, and aluminum. In particular, the present invention is related to monitoring and control of the electromagnetic forming process.
Electromagnetic forming is a process for shaping a metal product (called the workpiece) by means of the application of electromagnetic forces. Electromagnetic forming relies on the interaction of the magnetic field with the metal of the workpiece. The electromagnetic field is produced by passing an time varying electric current through a coil (called the workcoil). The current in the workcoil can be provided by the discharge of a capacitor (or more typically by a bank of capacitors) resulting in a pulsed output. The workpiece can be maintained at a temperature so that it is somewhat malleable to aid the forming process, although this is not necessary.
The electromagnetic forming process has several clear advantages. For example, there is no frictional contact between the workpiece and the field thereby allowing for a high quality finish on the workpiece. Also, the pulsed application of the electromagnetic field to the workpiece can be readily adapted to an automated "assembly line"-type process. Another advantage is that electromagnetic forming can be adapted to shapes for which it would be difficult to apply a solid mold wall.
Electromagnetic forming processes can typically have several different configurations. In one configuration, the workpiece surrounds the workcoil so the action of the field tends to expand or bulge the workpiece. In another configuration, the workcoil and workpiece are adjacent to each other so that the field bends the workpiece away from the workcoil. Another configuration has the workcoil surrounding the workpiece so that the field compresses the workpiece. In an example of this latter configuration, electromagnetic forming can be used to compress bands of metal on cylindrical-shaped molds.
Several factors limit the utility of the electromagnetic forming process. For example, since a relatively large electromagnetic pulse is necessary to form the metal, the coils and capacitors must be designed to accommodate such a pulse. Arcing of current across the turns of the workcoil or burnup of the capacitor can occur. Also, the coils and capacitors that are used may not be so precisely designed to produce a consistent electromagnetic force each time. Furthermore, other factors that can affect the amount of force applied to the workpiece include the temperature, thickness, and composition of the workpiece itself. It is for reasons such as these that electromagnetic forming has been used primarily in relatively simple applications with thin workpieces where solid molds can be used to define a boundary or otherwise limit application of the electromagnetic force.
It would enhance the utility of the electromagnetic forming process to be able to precisely control the application of the force of the electromagnetic field to the workpiece. However, even if greater control of the electromagnetic force produced by the workcoil were provided, the effect of the field on the workpiece is affected by factors related to the workpiece itself, such as composition, temperature, and dimensions of the workpiece. Therefore, in order to provide a electromagnetic forming process with a high degree of precision, it is necessary not only to precisely control the workcoil, but it is also necessary to be able to monitor the effects of the electromagnetic force on the workpiece during the application of the electromagnetic field to the workpiece. Such monitoring would be very advantageous to the electromagnetic forming process and would enable forming pieces of larger sizes and more complex shapes.
Inherent to all electromagnetic forming processes are electromagnetic fields which interact with the workpiece to provide a force which holds or shapes the work piece in some desired fashion. Contributions to the working electromagnetic field come from both the driving primary current source (workcoil) and the eddy currents induced in the workpiece. As a result, information regarding the instantaneous condition of the workpiece and the driving electronics are incorporated into the field in the form of amplitude, phase, and frequency. This information can be extracted using various electronic means and used to actively monitor or control the progress of the electromagnetic forming process.
In all processing techniques that use electromagnetic fields to physically form a solid or liquid metallic material, the electromagnetic fields contain the responses of the material to dynamic changes in the geometry, electrical conductivity, and magnetic permeability of the material during the processing. Therefore, monitoring the electromagnetic fields can provide information on the physical condition of the material being processed as well as the dynamics of the process itself. By directly monitoring the process via inherent or externally injected electromagnetic fields, means can be provided to actively monitor physical and metallurgical characteristics of the product such as geometry, cracking, temperature, and phase formation. This permits determination of the finished product's quality without the need for subsequent characterization or inspection steps, as well as providing information which can potentially be used to control the process in real time. Active process control may allow fabrication of products with increased physical and microstructural complexity.
Accordingly, it is an object of this invention to provide a monitoring and process control technique for electromagnetic forming processes based on the measurable interactions between the working electromagnetic fields and the material being processed.
It is another object of this invention is to use the electromagnetic fields inherent to electromagnetic forming techniques for the purpose of in-process control and monitoring.
Another object of this invention is to use the information contained in the responses of a workpiece to the field applied by the electromagnetic workcoil for monitoring of processes variables such as workpiece shape, temperature, defect formation, and phase change.
A further object of this invention is to provide a basis for feedback control algorithms for active control of electromagnetic forging which would permit dynamic control of force application and three dimensional displacement.
A yet further object of this invention is to provide the ability to control electromagnetic forming phenomena in real time to enhance the efficiency and capabilities of the electromagnetic forming technology.
Additional objects, advantages and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.